1. Field of the Invention
The present invention relates to a current supplying circuit which supplies an electric current for actuating an igniter at a time of actuation of an air bag gas generator, an air bag system using the current supplying circuit and a method of actuating an igniter.
2. Description of Related Art
An air bag system for protecting a passenger from an impact at a time of collision of a vehicle is indispensable, and the air bag system needs to be reduced in weight from a demand for reducing weight of an entire vehicle. Recently, kinds and the total number of air bags such as an air bag for a driver side, an air bag for a passenger side next to the driver, an air bag for a rear seat side, and an air bag for a side impact are increasing, and therefore, a lighter air bag system is in greater demand.
In a current air bag system, an electronic control unit (ECU) connected to a power source (a battery installed in a vehicle) and an impact detecting sensor are individually connected to individual gas generators (a gas generator and an air bag are accommodated in a module case). An aspect of the connection between the ECU and the individual gas generators is shown in FIG. 4.
As shown in FIG. 4, the ECU and each module case are connected to each other through two conducting wires (lead wires), and an electric current at a time of actuation of an igniter is supplied from a battery. When any one of the lead wires connecting the battery and the ECU at a time of vehicle collision is broken, a gas generator is not actuated. In order to avoid such a situation, a capacitor for backup power source is incorporated into the ECU. However, this capacitor has to actuate all igniters, and therefore, the capacitor is obligated to have a large capacitance (namely, weight), which makes the ECU so large.